The bead portion of the tire is a particularly critical component by reason of its role as the primary connector, as it were, between the wheel of the vertical and the ground-contacting tread.
Traditionally, bead members have been formed of metal wire which is combined with rubber in an extruding operation, followed by a forming of the bead ring with an appropriate number of winds of the metal wire and a wrapping of the assembly with a friction-coated textile wrap, otherwise known as bead stock.
Glass fibers have been suggested and employed in the manufacture of bead members. For example, U.S. Pat. Nos. 3,612,139 Marzocchi et al., 3,473,595 Marzocchi et al., and 3,237,674 Budd et al. teach using glass fibers as a tire bead reinforcement. As these references point out, glass cannot be simply substituted for another reinforcing material. The different properties and characteristics of the glass must be considered in the design. Furthermore, the geometry of the placement of the glass within the bead must be considered. It is believed that hoop stiffness is an important characteristic relating to the quality of bead performance in the tire. Hoop stiffness is the ability of the bead to resist deformation from its circular shape. A lack of sufficient loop stiffness of the bead is believed to have contributed to the peculiarities of early glass beads.
A sufficient degree of hoop stiffness is desirable for proper bead performance in a tire and for ease of handling during fabrication. The conventional all steel wire reinforced bead ring is generally much stiffer than is absolutely necessary.